Thermostatic control



Dec. 5, 1939.

E. L. ALDWORTH THERMOSTATIC CONTROL Filed July 24 1937 3 Sheets-Sheet lI I I l COLD E. L. ALDWORTH THERMOSTATIC CONTROL k nuanf'or Edda/(x7205L. tfldwarik By W M aw 2 Dec. 5, 1939. E. L. ALDWORTH THERMOSTATICCONTROL Filed July 24, 1957 3 Sheets-Sheet 3 Edward filafworffi PatentedDec. 5, 1939 UNITED STATES PATENT OFFICE THERMOSTATIC CONTROL Edward L.Aldworth, Grand Rapids. Mich.

Application July 24, 1937, Serial No. 155,375

10 Claims.

This invention relates to thermostatic controls of the general typeordinarily used for controlling heating and cooling systems forbuildings.

In general, thermostatic controls are subject to overrunning. That is,for example, in the case of a heater controlling the temperature ofbuilding, the thermostat is actuated when the building reaches a certainminimum temperature. The result of this actuation is that the heater isput 10 into operation so as to supply heat to the building, or in somecases the rate of supplying heat to the building is increased.Nevertheless there is a lag after the actuation of the thermostat duringwhich the temperature continues to decrease and this lag or overrunpersists until heat is being supplied to the building at the same rateat which it is lost. Thereafter the temperature rises and when itattains a certain point, the heater is rendered inoperative or isclamped.

20 Nevertheless there is a further overrun in which the temperatureincreases after the thermostat actuates the controls. The thermostat isnormally set to operate at temperature points which are spaced somewhatapart. Thus, the heater may be 25 turned on at 70 F. and may be turnedoif at 72 F. This temperature range in addition to the overrun, whenboth sides are off, provides a variation of temperature which isobjectionable.

According to the present invention, I provide 30 an improvedthermostatic control in which the overruns on both sides of thetemperature range for which the thermostatic device is set, areconsiderably diminished and in some cases completely eliminated. Myimproved thermostatic control is 35 adapted in most advantageouscircumstances to provide a slight variation of building temperaturewholly within, and in some cases, considerably less than the temperaturerange for which the control is set.

40 It must be understood that the thermostatic control is capable ofbeing used with any type of heater or cooler. Thus, in the case of gasor oil heat, the thermostat at one point puts the heater into operation,and at the other point terminates 45 the operation of the heater. Wheresolid fuel is used, the first point corresponds to the opening of thedrafts, and the second point corresponds to the closing of the drafts.In case the thermostatic control is used in connection with a cooling 50device, at one point it starts the supply of cold Fig. 1 is a more orless diagrammatic view of a thermostatic control according to myinvention;

Fig. 2 is a side elevation of the lower element thereof Fig. 3 is afront elevation of a further embodiment of my invention;

Fig. 4 is a side view thereof;

Fig. 5 is a plan view of a further embodiment of my invention;

Fig. 6 is a side elevation thereof; 10

Fig. 7 is a front elevation of a further embodiment of my invention.

Referring more particularly to Figs. 1 and 2, this embodiment ofmy'invention includes three thermostatic elements, H), II and i2, whichare 16 rigidly mounted at one end on bases l3, l4 and I5 respectivelyand are insulated therefrom. The free end of the thermostatic element I0is adapted to have a frictional engagement with a sector I6 which ispivotally mounted at I! on the base I3. 20

The sector l6 may be provided with stops I8 so as to limit the relativemovement of the thermostatic element l0 thereon. The periphery of thesector It carries a pair of projections I!) which are spaced in closerelation so as to receive between them the short end 20 of a lever 2|,which is pivotally mounted at 22. Owing to the shortness of the end 20of the lever 2|, which is quite long, the upper end of the lever 2|,which carries contacts 23, has a very considerable movement for a slightmovement of the lower end 20. The lever 2|, which is insulated from thebase I3, is connected to a conductor 24 which may include a battery 25or other source of electrical energy. Itmay here be noted that theconductor 24 may be the common wire of a three wire control system.

The contacts 23 and the lever 2| are adapted to move between stationarycontacts 26 and 21 respectively, which are mounted on the base I3 40 andinsulated therefrom and from each other. The contacts 26 and 21' arespaced apart so that only one of the contacts 23 is in engagement withthe contact 26 or the contact 21.

As the temperature falls, the thermostatic element i0 moves to the leftand owing to its frictional engagement with the sector IE, it carriesthe sector along with it to the left. The result is that the lever 2| isthrown to the right so as to bring one of the contacts 23 intoengagement with the contact 21. The contact 21 is connected by aconductor 28 to the thermostatic element I After the adjacent contact 23engages the contact 21, the movement of the lever 2| to the right isterminated and the thermostatic element the supply of heat.

86 may continue its movement to the left, slipping over the sector it.When the temperature is rising, the thermostatic element it moves to theright and the lever 2| is swung so as to bring the adjacent contact 23into engagement with the stationary contact 26. This stationary contact26 is connected by means of conductor 29 to the thermostatic element l2.After the contact 23 on the lever 2| engages the contact 26, the lever2i again ceases its movement and the thermostatic element l0 slides overthe stationary sector H6. The stops I8 prevent the thermostatic elementW from moving completely away from the sector H5 in unusualcircumstances. A

It may here be emphasized that owing to the shortness of the lower armof the lever 2i and the comparatively great length of the upper arm. ofthis lever, it will be seen that the contacts 23 are brought intoengagement with the appropriate contact 26 or 21 almost immediatelyafter the temperature begins to rise, or the temperature begins to fall,respectively.

The result is that the common wire 24 is connected to the thermostaticelement during falling temperature, and to the thermostatic element |2during rising temperature. The thermostatic element operates between twostationary contacts l2 and 14, which reference numbers I select becausethese points may be engaged, by the thermostatic element II attemperatures of 72 and 74 F., for example, the thermostatic element l2moves between two contacts 68 and 10, these members being selected forthe same reason, that is the thermostatic element |2 may engage thecontact 68 at a temperature of 68 F., and it mayengage the contact 10 ata temperature of 70 F. That is, the contacts associated with thethermostatic element define a higher range than those associated withthe thermostatic element l2.

The contacts 12 and 68 are connected to a conductor which I term theheat wire, and the contacts 14 and Ill are connected to a conductor 3|,which I term the cold wire. These terms are used merely as an aid toexplanation and are not intended to be limitative in anyrespect. In atypical installation, the conductor 24 when connected to the wire 30 bythe thermostatic control completes a circuit which starts the heater oractuates mechanism to increase When the circuit is made between the wire24 and the wire 3|, reverse operation occurs.

The operation of the device is as follows: It is assumed that thecontacts 12, I4, 68 and III are set so that they are engaged by theassociated thermostatic element at temperatures which correspondnumerically to these indicia on the Fahrenheit scale. If the temperatureis, for example 65, and the heater is operating so that the temperatureis increasing, then the thermostatic elements H and I2 are in their lefthand position, that is, they are in engagement with contacts 12 and 68respectively. Due to the movement of the thermostatic element Hi to theright under the influence of rising temperature, the lever 2| is broughtinto engagement with the stationary contact 26. Consequently, a circuitis completed from the battery 25, lever 2|, contact 26, conductor 29,thermostatic element I2, contact 68 and heat wire 30. This correspondsto the setting of the heater for the supply of heat. The supply of heat,therefore, continues until the temperature passes through 68 to '70".When the temperature 68 is reached, the therhot affect the heater.

- aisles? mostatic element l2 begins to move away from the contact 68towards the contact 16. This does The thermostatic element 52 engagesthe contact 70 at 70 F., completing a circuit through the thermostaticelement |2 between the conductor 24 and the cold wire 3|. This circuitactuates the heater so as to terminate or reduce its rate of supply ofheat. The temperature nevertheless proceeds to overrun, that is, thetemperature increases beyond 70 F. During this increase, control stillremains with the thermostatic element l2. At the end of the overrun,however, that is when the temperature begins to drop again, thethermostatic element i6, under the'infiuence of the falling temperature,promptly connects the wire 24 to the contact 21' and throws control overto the thermostatic element H. The degree of overrun varies inaccordance with the building and heating installation.

There are two general cases, however, that is, the overrun may not reachthe lower temperature, for example 72 F. of the higher rangethermostatic element H, or it may exceed that lower temperature. Toconsider the first case, when the overrun is terminated and control isthrown over to the thermostatic element II, that element, thetemperature being below 72", is in engagement with the stationarycontact 12 and the wire 24 is connected to the heat wire 30 so that theheater is started or its rate of supply of heat is increasedimmediately. Nevertheless due to the lag, the temperature continues tofall and eventually the temperature begins to rise again so that controlis again thrown over to the lower setting thermostatic element l2.

In the case under discussion, this ordinarily will occur before thetemperature of 70, that is the high temperature of the low settingthermostatic element I2, is reached. Consequently, the wire 24 isconnected to the cold wire 3| immediately when the changeover has beeneifected by the thermostatic element I0. It will thus be seen that inthis case the temperature remains between the lowest temperature pointof the thermostatic element II and the highest temperature point of thethermostatic element l2. Further in this case the heat is being suppliedalmost exclusively during the time the temperature is falling andpractically no heat is supplied during the time the temperature isrising. These effects contribute to a lessening of overrun and to theattainment of a more equitable temperature, or a temperature whichvaries within much closer limits than heretofore attainable Under idealcircumstances the range of tem-' perature permitted by the controlcoincides with the difierence of temperature between the minimum settingof the higher range thermostat and the maximum setting of the lowerrange thermostat; In these circumstances, the temperature range liesbetween these settings and all heat is supplied during fallingtemperature, and no heat is supplied during rising temperature, so thatthe smallest temperature range is attained.

In the case of certain installations which have a higher overrun, due toone cause or another, the operation is somewhat modified. Thus to give aconcrete example with the figures previously ascribed to the contacts12, 14, 68 and 10, it is assumed that the temperature is 65 and isincreasing. The thermostatic element l0 throws control to thethermostatic element I2. Since the temperature is below 68, thethermostatic element is in engagement with the contact 68 and the heatwire 30 is connected to the wire 24. This corresponds to the supply ofheat. When the temperature reaches 68 F. the thermostat l2 begins tomove away from the contact 68, which does not affect the heatingapparatus. When the thermostatic element l2 reaches the contact 10, thecold wire 3| is'put into circuit with the wire 24 and the heater isstopped or curtailed.

The overrun will carry thetemperature above 70 and in this specificinstance above the temperature of 72. During this overrun, the heater isstopped or damped. When the overrun terminates and the temperaturebegins to fall, control is then thrown by the thermostatic element Hi tothe thermostatic element ll. Since the temperature is above 72, thethermostatic element II is out of engagement with the contact 12.Consequently, the heater remains of! or in curtailed condition and thetemperature falls until 72 F. is reached whereupon the thermostat llengages the contact 12 and connects the conductor 24 to the heat wire 30so that the heater is put into operation or is accelerated.

In this particular instance, the temperature will ordinarily continue tofall to a point below 70 F. As the temperature falls, the thermostaticelement ll maintains engagement with contact 12. When the heat suppliedby this operation of the heater overcomes the tendency of thetemperature to drop, the temperature will begin to rise. The slightestincrease of the temperature will throw control over to the thermostaticelement l2. Since the temperature is below 70, the thermostatic element[2 is out of engagement with contact 10 so that the heating continuesuntil the temperature of 70 is attained. When that occurs, thethermostatic element l2 comes into engagement with the contact Ill andthe circuit is completed through thecold wire 3| so that the heater isterminated or curtailed.

The cycle just described is continued indefinitely, the temperatureoverrunning slightly below the maximum setting of the thermostaticelement I2 and overrunning slightly the minimum setting of thethermostatic element vI l. The heat is supplied'during the cycle fromthe temperature 72 to the minimum temperature and up to a temperature of70 again, that is it is.

supplied for the most part while the temperature is falling and to arelatively smaller extent while the temperature is rising. Thedistinctive manher in which heat is provided mainly while thetemperature is falling minimizes the tendency to overrun to a remarkabledegree. If any particular installation tends to overrun to an excessivedegree, such tendency may be minimized by increasing the separation ofthe settings of the two thermostats H and I2. Such increase augments theproportion of the heat which is supplied during falling temperature andhas the effect of decreasing the temperature range permitted by thecontrol.

Referring to the embodiment of the invention illustrated in Figs. 3 and4, it may be noted that the three thermostatic elements It, II and I2-move simultaneouslyso that they may be replaced by a single thermostaticelement It as shown in Figure 3. The thermostatic element It carries afriction plate 32 which is adapted to engage a sector l6 pivotallymounted at H and corresponding closely to the sector It in the firstdescribed embodiment of the invention. This sector cooperates with alever 2| in exactly the same way as previously described so that thislever is brought into engagement by the contact 26 when the temperatureis rising and is brought into engagement with the contact 21' when thetemperature is falling. The lever 2| is connected to a conductor 24'which includes the battery 25'. The thermostatic element l carries astrip of insulation 33 upon which are mounted two flexible contact armsI l' and i2 respectively. These flexible arms fulfill the functions ofthe thermostatic elements H and I2 previously described.

The resilient arm I I is adapted to engage contacts 12' and 14'. Theresilient arm I2 is adapted to engage contact 68' and 10'. Again thesereference numerals are employed to define an exemplary setting for thethermostatic control. That is, the resilient arm II will engage itscontacts at the ends of a range of temperature which is higher than therange at which the arm I2 engages its contacts. The contact 21' isconnected to the resilient arm H by means of a conductor 28'. Theresilient arm I2 is connected by a conductor 29' to the contact 26. Thesector Iii or the arms which carry it may be pro-. vided with stops I8to limit the freedom ,of movement of the thermostatic element l0 so asto maintain the resilient arms H and I2 at all times between theirassociated contacts. Arms II' and I2 are long and are very resilient incomparison to the thermostatic element I0. Consequently, the engagementof the arms II and I2 with their contacts will have no effect upon thenormal movement of the thermostatic element ill.

It will be obvious that when the temperature is falling, control will bethrown over to the arm II Just as it was to the thermostatic element l Iin the previously described embodiment, and that when the temperature isrising, control will bethrown over to the resilient arm l2 just as itwas thrown over'to the thermostatic control l2 in the previouslydescribed embodiment. The same results are, therefore, obtained inconnecting the wire 24' to the cold wire 3| and to the heat wire 30, asin the previously described embodiment.

' Figs. and 6 illustrate an embodiment of the invention in which mercuryswitches 34 and 35 are employed. Each switch includes a pair of contactsat each end and I have applied indicia to each pair of contactscorresponding to the exemplary temperatures at which they may becomeoperative, these temperatures being 72, 74, 68 and 70, corresponding tothe indicia used in the previously described embodiments.

The thermostatic element may suitably comprise a coil 36 of bi-metallicstrip, one end of the coil being secured to a base 31. The inner end ofthe coil 36 is'rigidly secured to a shaft 38. The shaft 38, which ishorizontal, has one end rotatably mounted in a bracket 39 and the otherend rotatably mounted in a bracket 40, both brackets being mounted onthe base 31. Rigidly mounted on the shaft 38 is a plate 4i with which afriction plate 42 is adapted to cooperate. The friction plate isyieldingly pressed toward the plate 4| by means of a spring 43 whichbears against the friction plate and against an abutment 44 which maysuitably be a block rigidly mounted on the shaft 38. The mercuryswitches 34 and 35 may suitably be carried in the block 44 atappropriate angles for operation in accordance with the temperaturesdesired for them. The friction plate 42 carries a projection 45 which islocated in a slot 44 on the short end of a lever.

41. The lever 41 is pivoted at 48 on a bracket 49 mounted on the base31. At the other end the lever 41 carries contacts, 50, one of which isadapted to engage a contact 5| or a contact 52 in extreme positions ofthe lever 41. The contacts 5| and 52 are mounted by means of insulationupon a bracket 58 mounted on the base 31.

When the temperature is falling, the plate 4| is rotated in a clockwisedirection as viewed from the right in Fig. 6, and consequently. thefriction plate 42 is rotated in the same direction and the lever 41 isswung so as to bring the adjacent contact and the lever 41 intoengagement with the contact 52. In other words, the contact 52corresponds to the contact 21 in the first described embodiment.

A rising temperature brings one of the contacts on the lever 41 intoengagement with the contact 5|. In other words, the contact 5|corresponds to the contact 28 of Fig. 1. The contact 5| is connected toone of each pair of contacts 68 and 18. The contact 52 is connected toone of each of the two contacts 12 and 14. The other of each pair ofcontacts." and 88 is connected to a wire 51 which is the heat wire. Theother of each pair of contacts 14 and 18 are connected to a wire 58which is the cold wire. The lever 41 is connected to a wire 58 which isthe common wire and contains a battery 60.

The manner in which this device operates will readily be understood fromconsideration of the previously described embodiment. There haspreviously been described the manner in which the shaft 88 is rotated inone direction or the other by change of temperature to make circuitthrough the contact 5| when the temperature is I rising, and through thecontact 52 when the temperature is falling. When the contact 5| isoperative, the temperature is rising and control is given to the mercuryswitch 84 which has the lower setting. When the temperature is falling,the circuit is made through the contact 52 and control is given to theswitch having the higher range. It will be understood that the electricswitches 34 and 35 are angularly displaced so that they will be actuatedto complete circuits at the appropriate temperatures.

Referring to the embodiment of the invention shown in Fig. 7, it is tobe noted that this embodiment comprises two thermostatic elements 8| and52. The thermostat 6| has a frictional contact with a sector 63 whichcontrols a pivoted lever, 84 in the manner previously described inconnection with the pivoted lever 2|. When the temperature is k lling,the lever 84 isswung into engagement with the stationary contact 85.When the temperature is rising, it is moved into engagement with thestationary contact 68. A conductor 81 is connected to the lever 64 andto one side of a battery 81. The other side of the battery 81 isconnected by means of conductor 88 to two resilient arms 92 and 93 whichare mounted-on and insulated from the plate 85 so as to project to theleft and right therefrom as best seen in Fig. 7. Beneath the resilientarms 92 and 93 are mounted in insulated relation two contact arms 94 and95. The contact arm 94 is connected to one end ofthe electromagnet 1|,the

. other end of which is connected by a conductor in any suitable mannerwithin a housing 98 in which the thermostatic element 62 is located. Themagnets may, for example, be supported upon the plate 85' by means ofbrackets. The

thermostatic element 82 operates between .two 8 contacts 15 and 18 whichare connected to a heat wire 11 and cold wire 18 respectively. Thethermostatic element 52 is connected to a common wire 19 which includesa battery 88'. The inner end of the thermostatic element 62 is rigidlymounted on a plate which is pivoted for free motion upon a pin 8|carried by the housing 98. The plate 88 carries two armatures 82 and 83which are adapted to cooperate with'the elec: tromagnets 59 and 1|respectively. Consequently when the electromagnet 68 is energized, the

thermostatic element 62 is thrown slightly to the left, as, viewed inFig. 7, and when the electromagnet 1| is energized, the thermostaticelement 62 is thrown somewhat to the right as viewed-in Fig. 7. Themovements ofthe plate 80 in either direction are limited by set screws84 carried on the plate 85 which is rotatably mounted upon the pin 8| asaxis and is located behind the plate 88. The plate 85 is heldfrictionally into any position in which it is located, and it comprisesa downwardly extending handle 86 whereby it may be moved to adjust thetemperature for which the thermostat is set.

This embodiment of the invention differs from those of the precedingembodiments in that control is exercised by one pair of contacts 15, 18instead of two pairs. I am enabled to, use one pair of contacts in thisembodiment of theinvention because I displace the thermostatic element82 to one side or to the other side in accordance with the prevailingchange of temperaturathat is, whether the temperature is rising orfalling. Thus when the electromagnet 89 is energized and thethermostatic element t2 is thrown to the left, then this element willengage the contact 15 at the temperature 72. When, however, thethermostatic element 62 is thrown tothe right, it'will not makeengagement with the contact 15 until the temperature of 68 is reached.When thus swung to the right, the thermostatic element 82 will engagethe contact 16 at '10". When plate 85 and to the plate 88 adjacent themounting of the thermostatic element 82. It will readily be seen in Fig.7 that in passing from one extreme to the other, this spring passes thepivot 8| upon which both plates 80 and 85 are mounted.

The operation of this embodiment of the invention is as follows: If thetemperature is fall-.

ing, the electromagnet 69 is energized and the thermostatic element 82is rendered of higher setting, that is, it completes a circuit throughthe heat wire at the minimum higher range temperature, which in theexamples is 72. When, however, the temperature is increasing, theelectromagnet 1| is energized and the thermostatic element 52 is movedtowards the cold contact 16. Consequently, since the temperature isrising and the thermostatic element is moving towards thatcontact 18,and it contacts it earlier than would have been the case had themechanical displacement oi! the thermostatic element 62 not been made.

It will readily be understood that the contact 15 and I6, and the othercontacts are adjustable and that these contacts may be brought into sucha. position that the thermostatic element 62 is moved from one to theother by the displacement due to the magnet 69 and II. Thus, forexample, if the temperature is falling, the thermostatic element 62 isthrown towards the left. When the temperature is below 12, the wire 11is in circuit and heat is produced. The overrun continues and is finallyterminated by the heat produced and the temperature then rises,effecting the energization of the electromagnet H and swinging of thethermostatic element 62 to the right. This movement to the right may besufficient to bring the thermostatic element 52 into engagement with thecontact 16 so that the cold wire 18 is energized and the heating isterminated or curtailed. When operating in this way, the ideal conditionis attained, that is the condition in which the heating is doneexclusively during falling temperature and is terminated or curtailedduring the period of rise in temperature.

The resilient arms 92 and 93 and the arms 94 and 95 are arranged to cutthe battery 81 out of circuit unless when the same is being actuallyused. Thus, the resilient arms 92 and 94 are shown in engagement in Fig.'7, whereas the arms 93 and 95 are out of engagement. Nocurrent is,therefore, flowing from the battery since the circuit of the magnet 69is open between the arms 93 and 95 and the circuit of the magnet I! isopen at the contact 66. When the lever 54 moves into engagement with thecontact 66, the circuit of the electromagnet H is energized, owing tothe fact that the arms 92 and 94 are in engagement. This engagementpersists until after the plate has swung through the dead centerposition, after which it opens, the complete movement of the. plate 80inthe clockwise direction being completed by the spring 9i. At the end ofthe movement, the arms 92 and 94 are out of engagement and the arms 93and 95 are in engagement, but the battery Bl is out of circuit since thelever is in its left hand position. The resilient arms 92 and 93 may beprovided with contact pieces 91 at their outermost ends whereby they maybe engaged by suitable portions of the swinging plate 80.

While the invention has been described in connection with three wirecontrol systems, that is systems having a heat wire, a cold wire, and acommon return wire, it is usually applicable to two wire control systemswhich include, for example, a heat wire and a return wire. In knowntwo-wire systems the heat may be on when the thermostat engages acontact and on when it separates from the contact. If the cold wire 35and lower contacts l9 and It are omitted from the apparatus shown inFig. 1, a two wire control system results in. which the thermostat iicontrols during falling temperature and the thermostat i2 controlsduring rising temperature. The same considerations apply to theembodiments of Figs. 3 and 4, and Figs. 5 and 6. In the case of theembodiment of Fig. '7, similar results may be obtained by omitting thecold wire 78 and contact 16.

Although the invention has been described in connection with thespecific details of a preferred embodiment thereof, it must beunderstood that such details are not intended to be limitative of theinvention except in so far as set forth in the accompanying claims.

I claim:

1. In combination, switches, a control circuit connected to bothswitches, a thermostatic element, switch means actuated by saidthermostatic element for connecting said circuit to one switch of thepair when the temperature is falling and to the other switch of the pairwhen the temperature is rising.

2. In combination, a thermostatic element, a second thermostaticelement, a contact adapted to be engaged by said second element, meansassociated with said second thermostatic element for moving it bodily tochange its relation to said contact, and means actuated by the firstsaid thermostatic element when the temperature starts to rise and startsto fall for operating said associated means to effect bodily movement ofsaid second thermostatic element.

3. In combination, a thermostatic element, a pair of contact memberscarried thereby, means insulating s "d contact members from each other,contacts apted to cooperate therewith, a conductor, and means responsiveto the initiation of rise and fall of temperature for connecting saidconductor selectively to one contact member or the other contact member.

4. In combination, a thermostat set for one temperature range, athermostat set for another range, circuit changing means adapted torender either of said thermostats operative, and means responsive to therising or falling of temperature for controlling said circuit changingmeans.

5. In combination, a thermostat, a pair of contacts adapted to cooperatetherewith, a second thermostat, a second pair of contacts adapted tocooperate therewith, a thermostatic element, a conductor, a switchadapted to connect the conductor to one thermostat or to the other, andmeans having a frictional contact with said element adapted to operatethe switch when the temperature begins to fall or rise.

6. In combination, a pair of thermostatic switches, a control circuitconnected to both elements, .9. thermostatic element, switch meanshaving a frictional engagement with said thermostatic element forconnecting the circuit to one of the first said pair of thermostaticswitches when the temperature begins to rise, and to the other switch ofsaid pair when the temperature begins to fall.

7. In combination, a thermostatic element, a second thermostaticelement, electromagnetic means associated with the last saidthermostatic element for changing the setting thereof, switching meansfor controlling said electromagnetic means, and means having africtional engagement with the first said thermostatic element foractuating the switching means when the temperature starts to fall andstarts to rise.

8. In combination, a thermostatic element, a pair of flexible contactarms carried thereby, fixed contacts adapted to cooperate therewith, aconductor, a switch adapted to connect said conductor selectively to oneof the flexible arms, and means having a frictional engagement with saidthermostatic element for actuating the switch in one direction when thetemperature starts to fall and in the other direction when thetemperature starts to rise.

9. In combination, a thermostatic element, a pair of switch membersmovable therewith in response to temperature change, a conductor,

a pair of thermostatic switching means adapted to connect said conductorto one switch member or the other, and means having a. frictionalconnection with said thermostatic element for actuating saidswitchmeans, a pair of switching means actuated thereby, switching meansfor rendering either of said pair of switching means operative and theother inoperative, and means immediately responsive to 5 ing means whenthe temperature starts to rise the initiation of rise and fall oftemperature for 6 and when the. temperature starts to fall. actuatingiast said switching means.

10. In combination, temperature responsive EDWARD L. ALDWORTH.

